Conventionally, charging and discharging of a rechargeable battery is adjusted to be performed within an appropriate range that is set based on the state of charge (SOC), which is an index indicating the charged state of the battery, to avoid excessive charging and discharging, which would deteriorate the battery performance. It is desirable that the SOC be calculated with high accuracy so that charging and discharging is performed within the appropriate SOC range. Patent document 1 describes a technique for measuring the voltage at a rechargeable battery, which is used for SOC calculation, with high accuracy.
Patent document 1 describes a battery voltage measurement circuit that includes a main capacitor, which is connected to two terminals of a rechargeable battery via an input-side semiconductor switch and charged by the rechargeable battery, and a differential amplification circuit, which is connected to the main capacitor via an output-side semiconductor switch. A sub-capacitor connects an output terminal and an inverting input terminal of the differential amplification circuit.